Study: Latest version of avian flu unlikely to cause pandemic

The avian H7N9 influenza virus that emerged earlier this year in China is poorly adapted for sustained transmission between humans, suggesting the current form of the virus is unlikely to cause a pandemic, according to a study.

As of Nov. 6, 139 confirmed human cases of avian H7N9 influenza, including 45 deaths, have been reported by the World Health Organization, according to background information in the study, which was published Dec. 6 in the journal Science. Most of these cases have been linked to exposure to infected poultry, but in some cases, limited human-to-human transmission might have occurred.

In the study, Ian A. Wilson, PhD, and James C. Paulson, PhD, of The Scripps Research Institute, and colleagues examined the three-dimensional structures of the hemagglutinin protein on the surface of the virus and its interaction with the human influenza receptor — the molecule on the surface of human cells that HA binds to before entering the cell and causing infection.

Previous research had shown that compared with influenza viruses that are adapted to spread easily among birds, viruses adapted to humans generally have different amino acids at the hemagglutinin protein site that recognize and bind to the human receptor. Recent studies have shown that certain H7N9 viruses had acquired mutations that might make them more adapted to humans.

However, using X-ray crystallography to study the hemagglutinin protein and receptor structures with unprecedented accuracy, the researchers demonstrated that the hemagglutinin protein in avian H7N9 influenza most closely resembles that of viruses that spread easily among birds, yet only weakly attaches to human influenza receptors.

Although the H7N9 virus conceivably could become transmissible from person to person, it would need to undergo multiple other mutations to do so, the study authors wrote.